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Advanced pyrotechnic and electronic components can be fabricated from Ni-based superalloys with hermetic seals to matched thermal expansion coefficient lithium-silicate glass ceramics (LSGC). Prior studies have characterized the interfacial reactions in these systems necessary for good chemical bonding. Similar interfacial reactions occur when LSGCs are bonded to 300-series stainless steel except that these seals debond on cooling to room temperature. We have found that Cr-depletion (from approximately 18 wt% to approximately 5 wt%) from the steel causes an fcc-to-bcc phase transition that expands the interfacial grains and decreases their thermal expansion coefficient, putting the LSGC into tension, causing the seal to fail. Linear elastic finite element calculations performed on a microcomputer suggest that the volume expansion associated with the phase transformation has a predominant effect compared with the difference in expansion coefficients.